Control system and process for application of energy to airway walls and other mediums

ABSTRACT

The present invention includes a system for delivering energy to an airway wall of a lung comprising an energy delivering apparatus and a PID controller having one or more variable gain factors which are rest after energy deliver has begun. The energy delivering apparatus may include a flexible elongated member and a distal expandable basket having at least one electrode for transferring energy to the airway wall and at least one temperature sensor for measuring temperature. The PID controller determines a new power set point base on an error between a preset temperature and the measured temperature. The algorithm can be P i+1 =P i +G(αe i +βe i−1 +γe i−2 ) where α, β and γ are preset values and α is from 1 to 2; β is from −1 to −2; and γ is from −0.5 to 0.5. In another variation, the controller is configured to shut down if various measured parameters are exceeded such as, for example, energy, impedance, temperature, temperature differences, activation time and combinations thereof. Methods for treating a target medium using a PID algorithm are also provided.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. patent application Ser. No.11/458,074, filed Jul. 17, 2006, now U.S. Pat. No. 7,854,734, which is acontinuation of U.S. patent application Ser. No. 10/414,411, filed Apr.14, 2003, now U.S. Pat. No. 7,104,987, which is a continuation ofInternational Patent Application No. PCT/US01/032321, filed Oct. 17,2001. U.S. patent application Ser. No. 10/414,411, filed Apr. 14, 2003,now U.S. Pat. No. 7,104,987, is also a continuation-in-part ofInternational Application No. PCT/US00/028745, filed Oct. 17, 2000, thecontents of which are hereby incorporated by reference in their entirety

TECHNICAL FIELD

This invention is related to systems for applying energy to lung airwaysand in particular, to a system and method for controlling the energydelivered to the airways using a PID algorithm to minimize error betweena preset temperature and a measured temperature.

BACKGROUND

Various obstructive airway diseases have some reversible component.Examples include COPD and asthma. There are an estimated 10 millionAmericans afflicted with Asthma. Asthma is a disease in whichbronchoconstriction, excessive mucus production, and inflammation andswelling of airways occur, causing widespread but variable airflowobstruction thereby making it difficult for the asthma sufferer tobreathe. Asthma is a chronic disorder, primarily characterized bypersistent airway inflammation. Asthma is further characterized by acuteepisodes of additional airway narrowing via contraction ofhyper-responsive airway smooth muscle.

Reversible aspects of obstructive pulmonary disease generally includeexcessive mucus production in the bronchial tree. Usually, there is ageneral increase in bulk (hypertrophy) of the large bronchi and chronicinflammatory changes in the small airways. Excessive amounts of mucusare found in the airways and semisolid plugs of mucus may occlude somesmall bronchi. Also, the small airways are narrowed and showinflammatory changes. Reversible aspects include partial airwayocclusion by excess secretions and airway narrowing secondary to smoothmuscle contraction, bronchial wall edema and inflammation of theairways.

In asthma, chronic inflammatory processes in the airway play a centralrole in increasing the resistance to airflow within the lungs. Manycells and cellular elements are involved in the inflammatory process,particularly mast cells, eosinophils T lymphocytes, neutrophils,epithelial cells, and even airway smooth muscle itself. The reactions ofthese cells result in an associated increase in the existing sensitivityand hyper-responsiveness of the airway smooth muscle cells that line theairways to the particular stimuli involved.

The chronic nature of asthma can also lead to remodeling of the airwaywall (i.e., structural changes such as thickening or edema) which canfurther affect the function of the airway wall and influence airwayhyper-responsiveness. Other physiologic changes associated with asthmainclude excess mucus production, and if the asthma is severe, mucusplugging, as well as ongoing epithelial denudation and repair.Epithelial denudation exposes the underlying tissue to substances thatwould not normally come in contact with them, further reinforcing thecycle of cellular damage and inflammatory response.

In susceptible individuals, asthma symptoms include recurrent episodesof shortness of breath (dyspnea), wheezing, chest tightness, and cough.Currently, asthma is managed by a combination of stimulus avoidance andpharmacology.

Stimulus avoidance is accomplished via systematic identification andminimization of contact with each type of stimuli. It may, however, beimpractical and not always helpful to avoid all potential stimuli.

Pharmacological management of asthma includes: (1) long term controlthrough use of anti-inflammatories and long-acting bronchodilators and(2) short term management of acute exacerbations through use ofshort-acting bronchodilators. Both of these approaches require repeatedand regular use of the prescribed drugs. High doses of corticosteroidanti-inflammatory drugs can have serious side effects that requirecareful management. In addition, some patients are resistant to steroidtreatment. The difficulty involved in patient compliance withpharmacologic management and the difficulty of avoiding stimulus thattriggers asthma are common barriers to successful asthma management.Current management techniques are thus neither completely successful norfree from side effects. Accordingly, it would be desirable to provide asystem and method which improves airflow without the need for patientcompliance.

Various energy delivering systems have been developed to intraluminallytreat anatomical structures and lumen other than the lung airways.Unfortunately, the systems which are useful in treating such structuresare generally not helpful in developing techniques to treat the lungairways because the lung airways are markedly different than othertissue structures. For example, lung airways are particularlyheterogeneous. Variations in lung tissue structure occur for a number ofreasons such as: the branching pattern of the tracheobronchial treeleads to local variation in the size and presence of airways; thevasculature of the lungs is a similar distributed network causingvariation in size and presence of blood vessels; within the airways arevariable amounts of differing structures such as cartilage, airwaysmooth muscle, and mucus glands and ducts; and energy delivery may alsobe influenced differently at the periphery, near the outer surface of alung lobe, than in the central portion.

Lung airways also include a number of protruding folds. Other tissuestructures such as blood vessels typically do not have the folds foundin airways. Airways contain mucous and air whereas other structurescontain different substances. The tissue chemistry between variouslumens and airways is also different. In view of these differences, itis not surprising that conventional energy delivering systems cannot beuniversally applied to treat all tissue structures. Moreover, powershut-offs and other safety mechanisms must be precisely tailored tospecific tissue so that the tissue is not harmed by application ofexcess energy.

Accordingly, an intraluminal RF energy delivering system that is capableof safely delivering RF energy to lung airways is desired. Inparticular, a system which is capable of controlling the temperaturewhen treating an airway of an asthma or COPD patient is desired. It isalso desirable to provide a system having built-in safeguards that shutthe power off thereby preventing damage to the subject tissue orcollateral tissue.

SUMMARY

The present invention includes a system for delivering energy to anairway wall of a lung comprising an energy delivering apparatus and aPID controller. The energy delivering apparatus may include a flexibleelongated member and a distal expandable basket having at least oneelectrode for transferring energy to the airway wall and at least onetemperature sensor for measuring temperature (T_(M)) of the airway wallwhen energy is delivered to the airway wall. The system furthercomprises a PID controller for determining a new power set point(P_(i+1)) based on an error (e) between a preset temperature (T_(S)) andthe measured temperature wherein the PID controller applies an algorithmhaving a variable gain factor (G).

In one variation of the present invention, the algorithm isP_(i+1)=P_(i)+G(αe_(i)+βe_(i−1)+γe_(i−2)) where α, β and γ are presetvalues. For instance, in one variation of the present invention, α isfrom 1 to 2; β is from −1 to −2; and γ is from −0.5 to 0.5. In anothervariation of the present invention, α, β, γ are 1.6, −1.6, and 0.0respectively.

In another variation of the present invention, the gain factor used inthe PID algorithm is reset 0.1 to 2 seconds after energy delivery hasbegun. The gain factor can also be reset 0.5 seconds after energydelivery has begun. The invention includes resetting G to 0.9 to 1.0 ifa temperature rise in ° C. per Joule is less than or equal to 2.5; 0.4to 0.5 if a temperature rise in ° C. per Joule is between 2.5 to 5.0; to0.2 to 0.3 if a temperature rise in ° C. per Joule is equal to 5.0 to7.5; and to 0.1 to 0.2 if a temperature rise in ° C. per Joule isgreater than 7.5. Initially, the gain factor is equal to 0.4 to 0.5 andpreferably 0.45 to 0.47.

In another variation of the present invention, the PID algorithm isP_(i+1)=P_(i)+(G₁e_(i)+G₂e_(i−1)+G₃e_(i−2)) and G₁, G₂ and G₃ arevariable gain factors. The invention includes configuring the controllersuch that G₁, G₂ and G₃ are reset to 0.9 to 2.00, −0.9 to −2.00 and 0.5to −0.5 respectively if a temperature rise in ° C. per Joule is lessthan or equal to 2.5; to 0.40 to 1.00, −0.40 to −1.00 and 0.25 to −0.25respectively if a temperature rise in ° C. per Joule is between 2.5 to5.0; to 0.20 to 0.60, −0.20 to −0.60 and 0.15 to −0.15 respectively if atemperature rise in ° C. per Joule is equal to 5.0 to 7.5; and to 0.10to 0.40, −0.10 to −0.40 and 0.10 to −0.10 respectively if a temperaturerise in ° C. per Joule is greater than 7.5. Each of the variable gainfactors may be equal to a product of at least one preset value and atleast one variable value.

In another variation of the present invention, the controller isconfigured such that the energy delivery is terminated if the energydelivered exceeds a maximum energy such as 120 joules.

In another variation of the present invention, the controller isconfigured to deliver energy for an activation time period such as up to15 seconds, 8 to 12 seconds, or 10 seconds.

In another variation of the present invention, the controller isconfigured such that Ts is set at a value between 60 to 80° C., or 65°C.

In another variation of the present invention, the controller isconfigured to measure impedance and said energy delivery is terminatedwhen said impedance drops below a preset impedance value such as 40 to60 ohms.

In another variation of the present invention, the controller isconfigured to terminate the energy delivery if T_(M) exceeds T_(S) by apre-selected value such as 10, 15 or 20° C.

In another variation of the present invention, the controller isconfigured to terminate the energy delivery if the output power isgreater or equal to a nominal output power and T_(M) drops by a criticaltemperature difference within a sampling period. The invention includesa nominal output power set at a value of at least 17 watts; the samplingperiod is set at a value of at least 0.5 seconds; and the criticaltemperature difference is 2° C.

In another variation of the present invention, the controller isconfigured to terminate the energy delivery if said T_(M) averaged overa time window exceeds T_(S) by a fixed temperature difference. The fixedtemperature difference may be a value between 1 and 10° C. or 5° C. Thetime window is between 1 and 5 seconds or 2 seconds.

In another variation of the present invention, the controller isconfigured to terminate if the measured temperature drops by 10 or more° C. in a sample period such as 1.0 seconds or 0.2 seconds.

Another variation of the present invention is a method for treating alung by transferring energy from an active region of an energy deliveryapparatus to an airway wall of the lung. The energy delivery apparatusincludes a flexible elongate body and a distal section and the activeregion is located in the distal section. The energy delivery apparatusfurther has a temperature sensor located in the distal section formeasuring a temperature (T_(M)) of said airway wall and the methodcomprises the following steps: setting a preset temperature (T_(S));determining a power set point (P_(i)) to deliver energy from the activeregion to the target medium; measuring the T_(M) using the temperaturesensor, and determining a new power set point (P_(i+1)) based on anerror (e) between the preset temperature (T_(S)) and the measuredtemperature (T_(M)) using a PID algorithm.

In yet another variation of the present invention, a process fortransferring energy to a target medium using an energy deliveryapparatus is provided. The energy delivery apparatus includes a flexibleelongate body and a distal section wherein the distal section includesan expandable basket with at least one active region for transferringenergy to the target medium. The energy delivery apparatus further has atemperature sensor located in the distal section for measuring atemperature (T_(M)) of the target medium. The process comprises thefollowing steps: setting a preset temperature (T_(S)); determining apower set point (P_(i)) to deliver energy from the active region to thetarget medium; measuring T_(M) using the temperature sensor; anddetermining a new power set point (P_(i+1)) based on an error (e)between the preset temperature (T_(S)) and the measured temperature(T_(M)) using an algorithm having a variable gain factor. The energy maybe delivered to an airway wall of a lung in vivo, in vitro or to anothertarget such as a sponge or towel which may be moistened with salinesolution. Saline solution increases the conductivity of the target.

In one variation of the present invention, the algorithm isP_(i+1)=P_(i)+G(αe_(i)+βe_(i−1)+γe_(i−2)) where α, β and γ are presetvalues: α is from 1 to 2; β is from −1 to −2; and γ is from −0.5 to 0.5.In another variation of the present invention, α, β, γ are 1.6, −1.6,and 0.0 respectively.

In another variation of the present invention, the gain factor is reset0.1 to 2 seconds after energy delivery has begun. The gain factor canalso be reset 0.5 seconds after energy delivery has begun. The inventionincludes resetting G to 0.9 to 1.0 if a temperature rise in ° C. perJoule is less than or equal to 2.5; 0.4 to 0.5 if a temperature rise in° C. per Joule is between 2.5 to 5.0; to 0.2 to 0.3 if a temperaturerise in ° C. per Joule is equal to 5.0 to 7.5; and to 0.1 to 0.2 if atemperature rise in ° C. per Joule is greater than 7.5. Initially, thegain factor is equal to 0.4 to 0.5 and preferably 0.45 to 0.47.

In another variation of the present invention, the energy delivery isterminated if the energy delivered exceeds a maximum energy such as 120joules.

In another variation of the present invention, energy is delivered foran activation time period such as 0 to 15 seconds, 8 to 12 seconds, or10 seconds.

In another variation of the present invention, T_(S) is set at a valuebetween 60 to 80, or 65° C.

In another variation of the present invention, impedance is measured andenergy delivery is terminated when the impedance drops below a presetimpedance value such as 40 to 60 ohms.

In another variation of the present invention, the energy is terminatedif T_(M) exceeds T_(S) by a pre-selected value such as 10, 15 or 20° C.

In another variation of the present invention, energy is terminated ifthe output power is greater or equal to a nominal output power and T_(M)drops by a critical temperature difference within a sampling period. Invariations of the present invention, the nominal output power is set ata value of at least 17 watts; the sampling period is set at a value ofat least 0.5 seconds; and the critical temperature difference is 2° C.

In another variation, the energy delivery apparatus is configured todeliver an amount of power up to a maximum power. The maximum power canbe from 10 to 40 watts and preferably from 15 to 20 watts.

In another variation of the present invention, energy delivery isterminated if T_(M) averaged over a time window exceeds T_(S) by a fixedtemperature difference. The fixed temperature difference may be a valuebetween 1 and 10° C. or 5° C. The time window is between 1 and 5 secondsor 2 seconds.

In another variation of the present invention, the energy delivery isterminated if the measured temperature drops by 10 or more ° C. in asample period such as 1.0 seconds or 0.2 seconds.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in greater detail with reference tothe various embodiments illustrated in the accompanying drawings:

FIG. 1 is a block diagram of a feedback loop of the present invention.

FIG. 2A is a cross sectional view of a medium sized bronchus in ahealthy patient. FIG. 2B is a cross sectional view of a bronchiole in ahealthy patient.

FIG. 3 is a cross sectional view of the bronchus of FIG. 2A showing theremodeling and constriction occurring in an asthma patient.

FIG. 4 is an illustration of the lungs being treated with a device andcontroller according to the present invention.

FIG. 5A is an illustration of an energy delivery device in accordancewith the present invention.

FIGS. 5B-5D show a partial view of a thermocouple attached to a basketleg in accordance with the present invention.

DETAILED DESCRIPTION

The present invention includes a controller and an energy deliverapparatus to deliver energy to the airway walls of the lungs. Amongstother features, the controller includes a feedback loop having avariable gain factor as diagramed in FIG. 1. The system is useful intreating asthma and various symptoms of reversible obstructive pulmonarydisease. Examples of suitable applications and methods are disclosed inInternational Application No. PCT/US00/28745 filed Oct. 17, 2000.

The present invention is particularly useful in treating lung tissue.This is surprising in view of the unique and complicated structure oflung tissue. Referring first to FIGS. 2A and 2B, a cross section of twodifferent airways in a healthy patient is shown. The airway of FIG. 2Ais a medium sized bronchus having an airway diameter D1 of about 3 mm.

FIG. 2B shows a section through a bronchiole having an airway diameterD2 of about 1.5 mm. Each airway includes a folded inner surface orepithelium 10 surrounded by stoma 12 and smooth muscle tissue 14. Thelarger airways including the bronchus shown in FIG. 2A also have mucousglands 16 and cartilage 18 surrounding the smooth muscle tissue 14.Nerve fibers 20 and blood vessels 24 surround the airway. The airway isthus quite different from other tissues such as blood vessel tissuewhich does not include such folds, cartilage or mucous glands. Incontrast, FIG. 3 illustrates the bronchus of FIG. 2A in which the smoothmuscle 14 has hypertrophied and increased in thickness causing theairway diameter to be reduced from the diameter D1 to a diameter D3.Accordingly, the airways to be treated with the device of the presentinvention may be 1 mm in diameter or greater, more preferably 3 mm indiameter or greater.

FIG. 4 is an illustration of the lungs being treated with a system 36according to the present invention. The system 36 includes a controller32 and an energy treatment device 30 which may be an elongated member asdescribed further below. The device 30 also includes an expandabledistal section which can be positioned at a treatment site 34 within alung or another target medium. In operation, the device is manipulatedto the treatment site 34. RF energy, for example, is delivered throughthe energy delivering device and penetrates the surface of the lungtissue such that tissue is affected below the epithelial layer as wellas on the surface of the lung tissue.

Energy Delivering Device

As indicated above, the present invention includes a controller 32 and adevice 30 through which it delivers energy to the target medium 34. Adevice 30 of the present invention should be of a size to access thebronchus or bronchioles of the human lung. The device may be sized tofit within bronchoscopes, preferably, with bronchoscopes having aworking channel of 2 mm or less. The device may also include a steeringmember configured to guide the device to a desired target location. Forexample, this steering member may deflect a distal tip of the device ina desired direction to navigate to a desired bronchi or bronchiole.

The energy delivering apparatus 30 typically includes an elongate bodyhaving a proximal section and a distal section. The distal sectionfeatures a radially expandable basket having a plurality of legs. Thelegs may be electrodes or have an active region defined by an insulatedcovering which contacts the medium to be treated. The basket is expandedwith an actuator mechanism which may be provided in a handle attached toproximal end of the elongate body. Examples of energy delivering devicesin accordance with the present invention are described in co-pendingU.S. application Ser. No. 09/436,455 filed Nov. 8, 1999 which is herebyincorporated by reference in its entirety.

Temperature Sensor

The invention also includes a temperature detecting element. Examples oftemperature detecting elements include thermocouples, infrared sensors,thermistors, resistance temperature detectors (RTDs), or any otherapparatus capable of detecting temperatures or changes in temperature.The temperature detecting element is preferably placed in proximity tothe expandable member.

FIG. 5A is a partial view of a variation of the invention havingthermocouple 137 positioned about midway along basket leg 106. FIG. 5Bis an enlarged partial view of the thermocouple 137 of FIG. 5A showingthe leads 139 separately coupled on an inwardly-facing surface of theleg 106. Consequently, the basket leg itself is used as part of thethermocouple junction upon which the temperature measurement is based.In other words, the thermocouple junction is intrinsic to the basketleg. This configuration is preferred because it provides an accuratetemperature measurement of tissue contacting the leg 106 in the vicinityof the thermocouple leads. In contrast, typical thermocoupleconfigurations consist of a thermocouple junction offset or extrinsic tothe basket leg. We believe that thermocouple junctions having an offsetfrom or extrinsic to the basket leg do not measure temperature asaccurately in certain applications as thermocouple junctions which areintrinsic to the basket leg.

The leads 139 may be placed at other locations along the leg 106including an edge 405. Joining the leads 139 to the edge 405, however,is undesirable because of its relatively small bonding surface.

FIG. 5B also shows basket leg 106 having an outer insulating material orcoating 410. The boundaries 415 of the insulating material 410 define anuninsulated, active section of electrode leg 106 which delivers energyto the tissue walls. Preferably, the insulating coating 410 is heatshrink tubing or a polymeric coating. However, other insulatingmaterials may be used.

FIGS. 5C and 5D show another variation of the present invention havingthin foil or laminated thermocouple leads 139. The thermocouple leads139 are configured as foils or layers which can be, for example,prefabricated foils or sputtered films. Suitable materials for thethermocouple leads (listed in pairs) include, but are not limited to:Constantan and Copper; Constantan and Nickel-Chromium; Constantan andIron; and Nickel-Aluminum and Nickel-Chromium. The thermocouple pair,CHROMEL and ALUMEL (both of which are registered trademarks of HoskinsManufacturing) is preferred. CHROMEL and ALUMEL is a standardthermocouple pair and has been shown to be biocompatible and corrosionresistant in our applications. The thermocouple leads 139 may be placedsuch that each lead approaches the center of the basket leg from anopposite end of the basket leg. The leads 139 then terminate in bondjoints 440 and 450. Alternatively, as shown in the configuration of FIG.5D, both thermocouple leads 139 may run from the same end of the basketleg 106.

Preferably, insulating layers 430 and 440 are disposed between the thinfilm leads 139 and the basket leg 106. The insulating layers 430 and 440electrically separate the leads 139 as well as electrically separate theleads from the leg 106. The insulating layers 430 and 440 limit thethermocouple junction to bond joints 450 and 460, which are optimallypositioned on active region 420 of basket leg 106.

Controller

The present invention includes a controller which controls the energy tobe delivered to the airways via an energy transfer device. Thecontroller includes at least one of the novel features disclosedhereinafter and may also incorporate features in known RF energycontrollers. An example of a RF generator which may be modified inaccordance with the present invention is the FORCE™ 2 Generatormanufactured by Valleylab, Boulder, Colo., U.S.A. Another suitabletechnique to generate and control RF energy is to modulate RF output ofa RF power amplifier by feeding it a suitable control signal.

The controller and power supply is configured to deliver enough energyto produce a desired effect in the lung. The power supply should also beconfigured to deliver the energy for a sufficient duration such that theeffect persists. This is accomplished by a time setting which may beentered into the power supply memory by a user.

The power supply or generator of the present invention can also employ anumber of algorithms to adjust energy delivery, to compensate for devicefailures (such as thermocouple detachment), to compensate for improperuse (such as poor contact of the electrodes), and to compensate fortissue inhomogeneities which can affect energy delivery such as, forexample, subsurface vessels, adjacent airways, or variations inconnective tissue.

The power supply can also include circuitry for monitoring parameters ofenergy. transfer: (for example, voltage, current, power, impedance, aswell as temperature from the temperature sensing element), and use thisinformation to control the amount of energy delivered. In the case ofdelivering RF energy, typical frequencies of the RF energy or RF powerwaveform are from 300 to 1750 kHz with 300 to 500 kHz or 450 to 475being preferred. The RF power-level generally ranges from about 0-30 Wbut depends upon a number of factors such as, size of the electrodes.The controller may also be configured to independently and selectivelyapply energy to one or more of the basket leg electrodes.

A power supply may also include control modes for delivering energysafely and effectively. Energy may be delivered in open loop (power heldconstint) mode for a specific time duration. Energy may also bedelivered in temperature control mode, with output power varied tomaintain a certain temperature for a specific time duration. In the caseof RF energy delivery via RF electrodes, the power supply may alsooperate in impedance control mode.

Temperature Control Mode

In a temperature control mode, the power supply may operate up to a 75°C. setting. That is, the temperature measured by the thermocouple canreach up to 75° C. before the power supply is shut off. The durationmust be long enough to produce the desired effect, but as short aspossible to allow treatment of all of the desired target airways withina lung. For example, up to 15 seconds is suitable, and more preferably 8to 12 seconds with about 10 seconds per activation (while the device isstationary) being preferred. Shorter duration with higher temperaturewill also produce an acceptable acute effect.

It should be noted that different device constructions utilize differentparameter settings to achieve the desired effect. For example, whiledirect RF electrodes typically utilize temperatures up to 75° C. intemperature control mode, resistively heated electrodes may utilizetemperatures up to 90° C.

Energy Pulses and Energy Modulation

Short bursts or pulses of RF energy may also be delivered to the targettissue. Short pulses of RF energy heat the proximal tissue while thedeeper tissue, which is primarily heated by conduction through theproximal tissue, cools between the bursts of energy. Short pulses ofenergy therefore tend to isolate treatment to the proximal tissue.

The application of short pulses of RF energy may be accomplished bymodulating the RF power waveform with a modulation waveform. Modulatingthe RF power waveform may be performed while employing any of the othercontrol algorithms discussed herein so long as they are not exclusive ofone another. For example, the RF energy may be modulated while in atemperature control mode.

Examples of modulation waveforms include but are not limited to a pulsetrain of square waves, sinusoidal, or any other waveform types. In thecase of square wave modulation, the modulated RF energy can becharacterized in terms of a pulse width (the time of an individual pulseof RF energy) and a duty cycle (the percent of time the RF output isapplied). A suitable duty cycle can be up to 100% which is essentiallyapplying RF energy without modulation. Duty cycles up to 80% or up to50% may also be suitable for limiting collateral damage or to localizethe affect of the applied energy.

Feedback Algorithm

As indicated above, the present invention includes controllers havingvarious algorithms. The algorithms may be either analog and digitalbased. A preferred embodiment is a three parameter controller, orProportional-Integral-Derivative (PID) controller which employs thefollowing algorithm: P_(i+1)=P_(i)+G(αe_(i)+βe_(i−1)+γe_(i−2)) whereP_(i+1) is a new power set point, P_(i) is a previous power set point,α, β and γ are preset values, G is a variable gain factor and e_(i),e_(i−1), e_(i−2) correspond to error at the present time step, error onestep previous and error two steps previous where the error is thedifference between the preset temperature and a measured temperature.

We have found that by using a variable gain factor (G) to adaptivelycontrol RF energy delivery, the system of the present invention cantreat a wide range of tissue types including lung tissue bronchus,bronchioles and other airway passages. The variable gain factor scalesthe coefficients (alpha, beta, and gamma; each a function of the threePID parameters) based on, for example, the temperature response toenergy input during the initial temperature ramp up.

Exemplary PID parameters are presented herein, expressed inalpha-beta-gamma space, for an energy delivering device and controllerof the present invention. These settings and timings are based ontesting in various animal lung tissues using an energy deliveringapparatus as described above. First, the gain factor preferably variesand is reset 0.1 to 2 and more preferably at 0.5 seconds after energydelivery has begun. Preferably, the gain factor is reset as follows: Gis reset to 0.9 to 1.0 and preferably 0.9 if a temperature rise in ° C.per Joule is less than or equal to 2.5; G is reset to 0.4 to 0.5 andpreferably 0.5 if a temperature rise in ° C. per Joule is between 2.5 to5.0; G is reset to 02 to 03 and preferably 0.2 if a temperature rise in° C. per Joule is equal to 5.0 to 7.5; and G is reset to 0.1 to 0.2 andpreferably 0.1 if a temperature rise in ° C. per Joule is greater than7.5. We have also found that a suitable value for α is from 1 to 2; forβ is from −1 to −2; and for γ is from −0.5 to 0.5. More preferably α, β,γ are 1.6, −1.6, and 0.0 respectively.

It is also possible to change the relative weights of alpha, beta, andgamma depending upon monitored temperature response working in eitherPID or Alpha-Beta-Gamma coordinate space beyond just scaling thealpha-beta-gamma coefficients with a variable gain factor. This can bedone by individually adjusting any or all of alpha, beta, or gamma.

In another variation of the present invention, the PID algorithm isP_(i+1)=P_(i)+(G₁e_(i)+G₂e_(i−1)+G₃e_(i−2)) and G₁, G₂ and G₃ are eachvariable gain factors. The invention includes configuring the controllersuch that G₁, G₂ and G₃ are reset to 0.90 to 2.00, −0.90 to −2.00 and0.50 to −0.50 respectively if a temperature rise in ° C. per Joule isless than or equal to 2.5; to 0.40 to 1.00, −0.40 to −1.00 and 0.25 to−025 respectively if a temperature rise in. ° C. per Joule is between2.5 to 5.0; to 0.20 to 0.60, −0.20 to −0.60 and 0.15 to −0.15respectively if a temperature rise in ° C. per Joule is equal to 5.0 to7.5; and to 0.10 to 0.40, −0.10 to −0.40 and 0.10 to −0.10 respectivelyif a temperature rise in ° C. per Joule is greater than 7.5. Each of thevariable gain factors may be equal to a product of at least one presetvalue and at least one variable value.

It is also possible to employ an algorithm that continuously adapts tosignals rather than at discrete sample steps, intervals or periods. Thealgorithm takes into account several variables upon which observedtemperature response depends including, for example: initialtemperature, time history of energy delivery, and the amount of energyrequired to maintain set point temperature. An exemplary analog PIDalgorithm is: u=K_(P)e+K_(I)∫edt+K_(D)(de/dt) where u is a signal to beadjusted such as, for example, a current, a voltage difference, or anoutput power which results in energy delivery from the electrode to theairway wall. K_(P), K_(I) and K_(D) are preset or variable values whichare multiplied with the proper error term where e(t) is the differencebetween a preset variable and a measured process variable such astemperature at time (t). The above equation is suitable for continuousand/or analog type controllers.

Power Shut Down Safety Algorithms

In addition to the control modes specified above, the power supply mayinclude control algorithms to limit excessive thermal damage to theairway tissue. Damage may be limited by terminating or shutting down theenergy being delivered to the target medium. The algorithms can be basedon the expectation that the sensed temperature of the tissue willrespond upon the application of energy. The temperature response, forexample, may be a change in temperature in a specified time or the rateof change of temperature. The expected temperature response can bepredicted as a function of the initially sensed temperature, thetemperature data for a specified power level as a function of time, orany other variables found to affect tissue properties. The expectedtemperature response may thus be used as a parameter in a power supplysafety algorithm. For example, if the measured temperature response isnot within a predefined range of the expected temperature response, thepower supply will automatically shut down.

Other control algorithms may also be employed. For example, an algorithmmay be employed to shut down energy delivery if the sensed temperaturedoes not rise by a certain number of degrees in a pre-specified amountof time after energy delivery begins. Preferably, if the sensedtemperature does not increase more than about 10° C. in about 3 seconds,the power supply is shut off. More preferably, if the sensed temperaturedoes not increase more than about 10° C. in about 1 second, the powersupply is shut off.

Another way to stop energy delivery includes shutting down a powersupply if the temperature ramp is not within a predefined range at anytime during energy delivery. For example, if the measured rate oftemperature change does not reach a predefined value, the power supplywill stop delivery of the RF energy. The predefined values arepredetermined and based on empirical data. Generally, the predefinedvalues are based on the duration of time RF energy is delivered and thepower-level applied. A suitable predefined rate of temperature change tostop energy delivery is from 8° C./second to 15° C./second in the first5 seconds (preferably in the first 2 seconds) of commencing energydelivery.

Other algorithms include shutting down a power supply if a maximumtemperature setting is exceeded or shutting down a power supply if thesensed temperature suddenly changes, such a change includes either adrop or rise, this change may indicate failure of the temperaturesensing element. For example, the generator or power supply may beprogrammed to shut off if the sensed temperature drops more than about10° C. in about 0.1 to 1 seconds and more preferably in about 0.2seconds.

In another configuration, the power is terminated when the measuredtemperature exceeds a pre-selected temperature or exceeds the set pointtemperature by a pre-selected amount. For example, when the set point isexceeded by 5 to 20° C., more preferably 15° C. the power willterminate.

In another configuration, power is terminated when the measuredtemperature (averaged over a time window) exceeds a pre-selectedtemperature. For example, power may be terminated when the measuredtemperature (averaged over 1 to 5 seconds and preferably averaged over 2seconds) exceeds the preset temperature by a predetermined amount. Thepredetermined amount is generally from 1 to 10° C. and preferably about5° C. Suitable preset temperatures are from 60 to 80° C. and mostpreferably about 65° C. Accordingly, in one exemplary configuration, thepower is stopped when the measured temperature (averaged over 2 seconds)exceeds 70° C.

In another configuration, the power is terminated when the amount ofenergy delivered exceeds a maximum amount. A suitable maximum amount is120 Joules for an energy delivery apparatus delivering energy to theairways of lungs.

In another configuration, the power is shut down depending on animpedance measurement. The impedance is monitored across a treated areaof tissue within the lung. Impedance may also be monitored at more thanone site within the lungs. The measuring of impedance may be but is notnecessarily performed by the same electrodes used to deliver the energytreatment to the tissue. The impedance may be measured as is known inthe art and as taught in U.S. application Ser. No. 09/436,455 which isincorporated by reference in its entirety. Accordingly, in one variationof the present invention, the power is adjusted or shut off when ameasured impedance drops below a preset impedance value. When using theenergy delivering device of the present invention to treat airways, asuitable range for the preset impedance value is from 40 to 60 ohms andpreferably about 50 ohms.

In another variation, the energy delivery apparatus is configured todeliver an amount of power up to a maximum power. The maximum power canbe from 10 to 40 watts and preferably from 15 to 20 watts.

In yet another configuration, the power supply is configured to shutdown if the power delivered exceeds a maximum power and the measuredtemperature drops by a critical temperature difference within a samplingperiod of time. A suitable maximum power is from 15 to 20 Watts andpreferably about 17 watts. The sampling period of time generally rangesfrom 0.1 to 1.0 seconds and preferably is about 0.5 seconds. A suitablerange for the critical temperature difference is about 2° C.

It is to be understood that any of the above algorithms and shut-downconfigurations may be combined in a single controller. However,algorithms having mutually exclusive functions may not be combined.

While the power supply or generator preferably includes or employs amicroprocessor, the invention is not so limited. Other means known inthe art may be employed. For example, the generator may be hardwired torun one or more of the above discussed algorithms.

The controller is preferably programmable and configured to receive andmanipulate other signals than the examples provided above. For example,other useful sensors may provide input signals to the processor to beused in determining the power output for the next step. The treatment ofan airway may also involve placing a visualization system such as anendoscope or bronchoscope into the airways. The treatment device is theninserted through or next to the bronchoscope or endoscope whilevisualizing the airways. Alternatively, the visualization system may bebuilt directly into the treatment device using fiber optic imaging andlenses or a CCD and lens arranged at the distal portion of the treatmentdevice. The treatment device may also be positioned using radiographicvisualization such as fluoroscopy or other external visualization means.

EXAMPLES

A system to treat airways in accordance with the present invention wasbuilt and tested in vivo on two canines. The system included an energydelivering apparatus having a distal basket. The basket includedelectrode legs and a temperature sensor mounted to one of the legs. Thesystem also included a generator programmed to measure the temperaturechange per energy unit during the first half-second of treatment. A PIDgain factor was adjusted depending on the measured tissue response. Thatis, the gain factor was adjusted based on the temperature change perjoule output during the first half second. In general, this correspondsto a higher gain for less responsive tissue and lower gain for moreresponsive tissue.

After treating the test subjects with a general anesthetic, RF energywas delivered to target regions using an energy delivery device andgenerator as described above. In particular, energy activations wereperformed on all available intraparenchyma 1 airways three millimetersor larger in diameter in both lungs. Three hundred sixty-threeactivations using a 65° C. temperature setting were performed in the twoanimals (i.e., 180 activations per animal). Additionally, in twenty ofthe activations in each animal, the energy delivery device wasdeliberately deployed improperly to provide a “Stress” condition.

In each activation, the measured temperature reached and stabilized at65° C. or, in the case of the twenty activations under “stress”conditions, the power properly shut off. Thus, the present invention cansuccessfully treat lung tissue with a variable gain setting and varioussafety algorithms to safely maintain a preset temperature at theelectrode or lung tissue surface. This temperature control isparticularly advantageous when treating the airways of lungs to reduceasthma symptoms.

This invention has been described and specific embodiments or examplesof the invention have been portrayed to convey a proper understanding ofthe invention. The use of such examples is not intended to limit theinvention in any way. Additionally, to the extent that there arevariations of the invention which are within the spirit of thedisclosure and are equivalent to features found in the claims, it is theintent that the claims cover those variations as well. All equivalentsare considered to be within the scope of the claimed invention, eventhose which may not have been set forth herein merely for the sake ofbrevity. Also, the various aspects of the invention described herein maybe modified and/or used in combination with such other aspects alsodescribed to be part of the invention either explicitly or inherently toform other advantageous variations considered to be part of theinvention covered by the claims which follow.

The invention described herein expressly incorporates the followingco-pending applications by reference in their entirety: U.S. applicationSer. No. 09/095,323; U.S. application Ser. No. 09/095,323; U.S.application Ser. No. 09/349,715; U.S. application Ser. No. 09/296,040;U.S. application Ser. No. 09/436,455; and U.S. application Ser. No.09/535,856.

We claim:
 1. A system for delivering energy to an airway wall of a lungcomprising: an energy delivering apparatus comprising a flexibleelongated member and a distal expandable member, said expandable memberhaving at least one electrode for transferring energy to said airwaywall and at least one sensor for measuring a parameter of said airwaywall when energy is delivered to said airway wall; and a safetymechanism for automatically terminating the energy transferred from theelectrode to the airway wall based on the measured parameter, whereinthe measured parameter includes a rate of change of a temperatureassociated with tissue of the airway wall, wherein the safety mechanismis configured to terminate energy delivery when a sensed temperaturedoes not increase by at least 10° C. in an initial 3 seconds from aninitiation of energy delivery.
 2. The system of claim 1, wherein themeasured parameter includes energy delivered to the airway wall.
 3. Thesystem of claim 1, wherein the measured parameter includes an impedanceof tissue associated with the airway wall.
 4. The system of claim 3,wherein the impedance is measured by the at least one electrode.
 5. Thesystem of claim 3, further comprising a second electrode different fromthe at least one electrode, wherein the impedance is measured by thesecond electrode.
 6. The system of claim of 3, wherein the safetymechanism is configured to terminate energy transfer when the impedanceis below a preset impedance threshold.
 7. The system of claim 3, whereinthe impedance of tissue associated with the airway wall includesimpedance across a treated area of tissue.
 8. The system of claim 7,wherein the impedance of tissue associated with the airway wall includesimpedance measured at more than one site within the lung.
 9. The systemof claim 1, wherein the safety mechanism is configured to terminateenergy delivery when the sensed temperature does not increase by atleast 10° C. in an initial 1 second from the initiation of energydelivery.
 10. The system of claim 1, wherein the safety mechanism isconfigured to terminate energy delivery when a sensed temperaturechanges by at least 10° C. in a time period from 0.1 to 1 seconds at anypoint during energy delivery.
 11. A system for delivering energy to anairway wall of a lung, the system comprising: an energy deliveryapparatus including: an elongate shaft having a proximal end, a distalend, and a lumen extending therebetween; an expandable member disposedwithin the lumen, wherein the expandable member is configured totransition between a collapsed configuration when within the lumen andan expanded configuration when deployed out of the lumen, wherein theexpandable member includes an electrode for delivering energy to tissueassociated with the airway wall; a temperature sensor coupled to theexpandable member; and a safety mechanism configured to automaticallyterminate energy delivery in response to a rate of temperature changederived from a temperature sensed by the temperature sensor, wherein thesafety mechanism is configured to terminate energy delivery when asensed temperature changes by at least 10° C. in a time period from 0.1to 1 seconds at any point during energy delivery.
 12. The system ofclaim 11, wherein the energy delivered is configured to penetrate thesurface of the tissue to affect tissue below an epithelial layer of thetissue.
 13. The system of claim 11, wherein the safety mechanismincludes an algorithm programmed within a controller.
 14. The system ofclaim 11, wherein the system is configured to terminate energy deliverywhen the sensed temperature exceeds a predetermined threshold.
 15. Thesystem of claim 11, wherein the system is configured to terminate energydelivery when the rate of change of the sensed temperature exceeds apredetermined rate of change.
 16. The system of claim 11, wherein thesystem is configured to terminate energy delivery when the rate ofchange of the sensed temperature is less than a predetermined rate ofchange.
 17. The system of claim 11, wherein the safety mechanism isfurther configured to automatically terminate energy delivery inresponse to a sensed impedance.
 18. A system for delivering energy to anairway wall of a lung comprising; an energy delivering apparatuscomprising a flexible elongated member and a distal expandable member,said expandable member having at least one electrode for transferringenergy to said airway wall; a temperature sensor configured to measure atemperature of one or more of the at least one electrode or airway wall;an impedance sensor configured to measure an impedance of the airwaywall; and a safety mechanism for automatically terminating the energytransferred from the electrode to the airway wall under each of thefollowing conditions: a sensed temperature by the temperature sensordoes not increase by at least 10° C. in an initial 1 to 3 seconds fromthe initiation of energy delivery; a sensed temperature exceeds a hightemperature threshold at any time during energy delivery, wherein thehigh temperature threshold is from 60° C. to 80° C.; a total amount ofenergy delivered to the airway wall in a single activation of the energydelivering apparatus is at least 120 joules; a determined rate oftemperature change derived from temperatures sensed by the temperaturesensor differs from an accepted rate of temperature change; a fault ofthe temperature sensor is determined; and a sensed impedance by theimpedance sensor is below an impedance threshold.